Dehalogenating dimerization and codimerization of beta-halogenated organic compounds



United States Patent 3,536,747 DEHALOGENATING DIMERIZATION AND CODIMERIZATION 0F fl-HALOGENATED ORGANIC COMPOUNDS Pierre Mathis, Brussels, and Leon Vanmelkebeke, Wezembeek, Oppem, Belgium, assignors to Solvay & Cie, Brussels, Belgium, a Belgian corporation No Drawing. Filed June 7, 1967, Ser. No. 644,061 Claims priority, application France, June 9, 1966,

64,857; May 9, 1967, 105,721 Int. Cl. C07c 121/20, 121/26 US. Cl. 260-4653 11 Claims ABSTRACT OF THE DISCLOSURE The dehalogenating dimerization and codimerization of fl-halogenated organic compounds is carried out by contacting with an alkaline or alkaline earth amalgam a solution of the li-halogenated organic compounds in an organic solvent which is inert towards the amalgam under the reaction conditions and which has a high dielectric constant.

BACKGROUND OF THE INVENTION This invention relates to a dimerization and codimerization process for the dehalogenation of B-halogenated organic compounds of the general formula in which Hal represents a halogen atom, R and R stand for hydrogen or a hydrocarbon group and X is a nitrile or an ester group.

More particularly, the invention is directed to the dimerization and the codimerization of 13-halogenated nitriles and ti-halogenated propionic acid esters which may be substituted in the a-position.

The dehalogenation of a El-halogenated propionic compound by dimerization in the presence of an alkali metal or an alkaline earth metal amalgam is an application of a well known type of reaction, the Wurtz reaction. The dimerization of fi-chloropropionitrile into adiponitrile by means of a potassium amalgam is described in German Pat. No. 1,151,791. Because of low yields and a low conversion rate, this process can hardly be used on an industrial basis. The rate of conversion of the B-chloroprm pionitrile is only about 7% per hour; the total adiponitrile yield is 37.8% and the percentage of potassium which is used for dimerizing the ,B-chloropropionitrile is only 23%.

The above German patent indicates that the yield may be improved by using a mixture of acrylonitrile and of a fl-halogenated propionitrile. The concentrations of the two reactants in the mixture are respectively to 80% molar, preferably 20 to 50%, and 20 to 90% molar, preferably 50 to 80%. In this process, the adiponitrile yield is relatively high, reaching 90.2% at the maximum, but the proportion of the active metal which is utilized is only 59% at the maximum. Furthermore, the conversion rate is very low.

SUMMARY OF THE INVENTION A new process has now been developed in which it is possible to obtain high conversion rates and, at the same Patented Oct. 27, 1970 ice in which Hal represents a halogen atom, R and R stand for hydrogen or a hydrocarbon group and X is a nitrile or an ester group, may be carried out by mixing an alkali metal or an alkaline earth metal amalgam with a solution of the [i-halogenated organic compounds in an organic solvent which is inert towards the amalgam under the usual reaction conditions, and which has a high dielectric constant.

For example, solvents which liberate protons, such as acids, alcohols, and solvents containing halogens in their molecule are not suitable in the process according to the invention. The solvents which may be used, according to the invention, should have a reactivity lower than the B- halogenated organic compound with respect to the amalgam, in order to be inert under the conditions of operation. Through their molecular arrangement, the solvents should be capable of solvating the cations. Their dielectric constant measured at room temperature (20 C.) is generally higher than 20.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following table is a list of typical solvents having a high dielectric constant. Among these solvents, those which are inert towards the amalgam, under the conditions of operation, may be used in the process according to the invention.

Inert with Temperature respect C.) at

to the which e was Dielectric Solvent amalgam? measured constant, e

Methanol N0 20 33.5 No 20 25 No 20 38. 5 No 20 41 20 41. 7 Dimethylsulfate Yes 20 55 Dimethylsulfoxide Yes 25 46.5 Tetramethylenesulfone Yes-.. 30 44 N 20 38. 5 20 35. 5 2,2-dinitro-propane No 20 35 Acetone Yes 20 20. 5 Acetamide Yes. 20 59 N-methylformamide Yes. 20 N,N-dimethylformam1d Yes- 20 37. 5 N-methylacetamide Yes. 20 175.5 N N-dunethylaeetamide Yes-.- 20 39 N-methylpropionamide Yes- 2%82 Epichlorhydrin No 3 stant could also be used in the process according to the invention.

The proportion of the solvent in the starting solution should be from 0.04 to liters of solvent per mole of fl-halogenated organic compound, preferably from 0.05 to 2 liters of solvent per mole.

The amalgam which is used to carry out the dimerization process, generally contains from 0.1 to 10 grams of active metal per kilogram of mercury, preferably between 0.5 to 7 g./kg. An amalgam produced by the electrolysis of alkaline halides in mercury cathode cells can be used with advantage.

With an amalgam produced by electrolysis, it is not necessary to exhaust it entirely during the dimerization process, since it may be easily reintroduced at an intermediate level in the electrolysis cell.

The conversion rate and the yields are improved by adding a small quantity of water to the reactive mixture. This quantity should be kept within narrow limits in order to prevent exhausting of the amalgam and the production of hydrogen. The quantity of water should generally be from 0.05 to of the weight of the solution, preferably from 1 to 10%.

The dehalogenating dimerization reaction is carried out at the interface between the amalgam and the reactive mixture. It is recommended to increase the surface, for example, by introducing the amalgam as fine droplets. The interface may also be increased by agitating the two phases, especially the organic phase where the diffusion is slow.

The reaction temperature may vary from 0 to 150 C., preferably from to 140 C. Generally, the reaction is carried out at atmospheric pressure and at a temperature below the boiling point of the solvent. The best results have been obtained at temperatures from to 70 C.

The process according to the invention is particularly useful for the dimerization and the codimerization of [3- halogenated propionitriles and of the esters of [it-halogenated propionic acid. These compounds may be easily produced by the hydrohalogenation of the corresponding nitriles and acrylic esters. The dimers and codimers so produced are particularly useful as monomers for the production of nylons. The dehalogenating dimerization of fl-halogenated propionitriles produces adiponitrile which may thereafter be hydrogenated into hexamethylene diamine or hydrolyzed into adipic acid. Both these compounds are well known monomers used for the production of nylon-6,6. On the other hand, the fi-halogenated propionio acid esters are not only capable of being dimerized with the formation of adipates, which may be substituted, but may also be codimerized with other B-halogenated propionic compounds, particularly the nitriles. In this case, besides the two usual adipate and adiponitrile dimers, there is produced a predominating proportion of a mixed dimer, or of a codimer which is the w-cyanopentanoate.

This compound may be hydrolyzed into adipic acid or it may be hydrogenated into w-aminocaproate which is a monomer used in the production of nylon-6.

fl-Chloropropionitrile is a B-halogenated propionitrile which is particularly suitable to dimerization or codimerization according to the process of the invention. It may be easily produced by the addition of a molecule of hydrogen chloride to a molecule of acrylonitrile (J. Am. Chem. Soc., vol. 69, p. 713 and 714, 1947).

Similarly, a B-halogenated propionic acid ester which is particularly suitable for dimerization or codimerization, according to the process of the invention, is methyl [3- chloropropionate which is easily obtained by the addition of one molecule of hydrogen chloride to methyl acrylate.

In the dimerization of the fl-halogenated propionitriles, after termination of the reaction, in addition to adiponitrile and fi-halogenated propionitrile which has not reacted, propionitrile and acrylonitrile are present. The production of acrylonitrile has no effect On the yield of the reaction. On the contrary, this compound may be easily recycled for the production of fi-halogenated propionitrile.

It is not necessary to separate the acrylonitrile fraction which is still present in the fi-halogenated propionitrile before carrying out the dimerization reaction.

It has indeed been realized that when the concentration of acrylonitrile in the reaction mixture is increased by incorporating, at the start, a small supplementary quantity of acrylonitrile which is added to the quantity which is formed during the dimerization reaction, the yields and the rate of reaction are improved. The quantity of acrylonitrile which is added to the starting reactive mixture may be from 0.001 to 1 mole per mole of ,B-halogenated propionitrile. Preferably, from 0.01 to 0.50 mole per mole of the halogenated nitrile is used. Moreover, it is found that the foregoing applies with respect to the addition, to the solution of any B-halogenated organic compound reacted according to the present invention, of the corresponding txfi-dehydrohalogenated compound.

The process according to the invention is preferably carried out continuously and coordinated with the produc tion of the B-halogenated organic compound and with an electrolysis by means of a mercury cathode. There are some advantages in further coordinating these operations by having recycling stages between them.

In the dimerization of ,B-chloropropionitrile, when the aforementioned three processes are combined the total reaction can be written in the following manner:

ZCH CHCN +2HCl- CN CH CN C1 In the first stage which is the hydrochlorination of acrylonitrile, the following reaction is carried out:

The [i-chloropropionitrile is thereafter subjected to dechlorinating dimerization according to the following reaction:

Furthermore, there is production of acrylonitrile which is recycled with the excess fi-chloropropionitrile to the start of the hydrochlorination or to the start of the dimerization stage. All the sodium which is used can be recovered as sodium chloride which is recycled to the electrolysis tubs, with the result that the total process does not use sodium and produces chlorine. It is obvious that the sodium amalgam does not have to be completely exhausted if the electrolysis has a higher capacity than is necessary for regenerating the amalgam.

To summarize, starting from acrylonitrile, hydrogen chloride, electric energy and eventually heat, adiponitrile and chlorine are produced. Contrary to the usual dimerization process for hydrogenating acrylonitrile, there is no production of caustic soda.

The invention will now be further described by reference to the following examples which are intended to illustrate but not to limit the invention.

Examples 1 to 4 A number of discontinuous tests were carried out in glass cylindrical reactors all having the same height (350 mm.) but having different diameters depending on the volume of the organic phase which is introduced therein.

A sodium amalgam which is pulverized into droplets having a diameter of approximately 0.5 mm. by means of a perforated porcelain plate, is brought at the top of a reactor by means of a constant flow pump (approximately 66 kg./hour). The droplets fall freely into the reaction mixture. The amalgam having a decreased content of active metal is recovered at the bottom of the reactor and is recycled by means of the pump. The assembly is main tained at a constant temperature.

Reactive solutions having various ,B-chloropropionitrile, solvent and water concentrations are introduced into the reactor. The concentration and the nature of the solvent;

are specified in Table I. In the same table, the quantities and the concentrations in sodium in the amalgam and the temperature and duration of the reaction are also given. The tests carried out as references (comparative examples) have been numbered by a reference numeral vention. Example 3 shows that the adiponitrile yield with respect to fi-chloropropionitrile and sodium and the conversion rate are clearly improved by adding a small quantity of water in addition to the solvent.

preceded by the letter R. 5 Examples 5 to 14 The adiponitrile, fl-chloropropionitrile and acrylonitrile concentrations are determined by gaseous chromatogra- A senes of tests was earned out continuously in a bellphy. The results of the analysis are given i Table II. The shaped reactor eontemmg an ergame phase and in which molar quantity of fi-chloropropionitrile which is converted the towel P 15 Immersed 111 e 505111111 amalgam The during the reaction is considered to be equal to the molar 0f the Interface 18 28 f e c ions at the quantity of the starting compound minus the quantity 1nterface are continuously renewed by means of an agrwhich is found intact in the end mixture, and also minus tator whlch operates simultaneo s y 111 the amalgam and the quantity corresponding to the acrylonitrile found in 111 the ofgehle Ph which has the hlghest letetloh the end mixture which is easily converted quantitatively Speed POSSlble wfthout dlspefslng the amalgam- The into fl-chloropropionitrile. This quantity is equal to twice fl w of the reaetlon mlxture at the Input 18 as y the number of moles of adiponitrile which has been a rotameter- The cream phase and the amalgam whleh f r d, in d by th mb f moles f phlor are introduced contmuously into the reactor are evacupropionitrile which has reacted for the production of nonated y Overflow The assembly 18 malntained at a 60 recoverable by-products comprising, in greater part, pro- 20 Stallt temperature. pionitrile. The molar adiponitrile yields have been cal- The Input flew 0f the ofgehle Phase compohehts and culated keeping in mind that two moles of B-chloropro- 9 the amalgam and the feeetleh temperature are glveh pionitrile are required for the formation of one mole of 111 Table The tests earned out y y Of reference adiponitrile have been g1ven an example number preceded by the According to the total quantity of sodium which has lettel been used during the reaction, the proportion of reacted Table IV gives the test e e adlpohltflle 1110131 sodium which was used for the dimerization of the p-chlo- Yleld 1S t y keePlhg 111 mind t two moles ropropionitrile has been determined by taking into act fifehlotopfoplomtl'lle corfespohtt to one mole of p count the fact that two gram-atoms of sodium are renltrlle eh expressed as a Tatlo 0f the quelltlty 0f quired to produce one mole of adiponitrile. adlpehltule melee) ed every hour and of the Finally, the reaction rate has been obtained by meaS; q y 0f fi' p p defihltely v rt d per uring the quantity of fl-chloropropionitrile converted h0ur. As 1n the preceding examples, the acrylonitrile every hour, which is formed is considered to be recoverable.

TABLE 1 Composition of the starting solution Sodium amalgam R a ti diti BChloropropio Weight Weight nitrile Identity Solvent Water Sodium of of Number of Tempera- Example (a) of content content content amalgam sodium g.-atorns ture Duration No. (mmole) solvent (ml) (g.) (g./kg) (kg.) (g.) of sodium (C.) (hours) 1, 700 .0 15. 74 78. 7 3. 42 120 4 625 Benzene 195 4- 9 8.752 43.0 1.87 70 14.5 590 Dimethylformamide 166 4. 94 6.375 31.5 1.37 70 a 1,310 Formamide 310 5.24 11.861 62.0 2.695 70 3 630 Dimethylformamide" 177 5.13 6.370 32.6 1.42 70 2 630 do 177 4.98 7.344 36.6 1. 59 3.33

TABLE II Composition of the end solution fi-ch'lorqiiiiy T t 1 i 10111 11 8 0 a O- c onverted B-chloropro- Prectlcal 111E41 Conversloh Unchanged into nonpionitrile z p l ield fete, B-chlororecoverable definitely adlpommle adipomtnle Sodium with Percent Adipupropio- Aerylolay-products converted zbxloo w rt d respect t D 110111 Example nitrile (b) nitrile (c) nitrile (d) a(2b+c+d) a-(c-i-d) a-c 2-(c-l-d) (mg.- sodium N0. (mmole) (mmole) (mmole) (mmole) (mole) percent percent atoms) percent wt 41 1, 182 135 301 383 15. s 7. e 17. 3 339 145 107 141 12. 1 2 156 0 3 272 584 52.9 20 355. 5 0 3 59s 1, 307 54. 3 as. 3 254. 5 0 15 104 613 80. s 27s 0 3s 36 592 88.3 30

Reference Examples R1 and R2 show that when B-chloropropionitrile is dimerized in the absence of a solvent or in the presence of a solvent which is not in accordance with the invention, the molar adiponitrile yield and the conversion rate are low. According to Examples 1 and 2, the yields and the reaction rates are appreciably improved by the addition of a solvent according to the insurface of the two phases.

Every hour there is produced a liquid containing 155 mmoles of dimethyl adipate, '50 mmoles of methyl ,B-chloropropionate, 50 mmoles of methyl acrylate and 6 mmoles of methyl propionate.

The theoretical molar yield (calculated with respect to the converted B-chloropropionate) in dimethyl adipate is 98%, and the practical calculated yield, bearing in mind that the acrylate has also reacted, is 90.3%.

The dimer yields with respect to the sodium which has reacted are very close to 100%.

Example 17 Under conditions identical to those employed in Examples to 14, a test was carried out in which the fi-halogenated propionitrile was codimerized with an ester of a S-halogenated propionic acid.

The reaction temperature was 40 C.

Every hour there was introduced a mixture comprising 183.4 mmoles of methyl fl-chloropropionate, 157.7 mmoles of B-chloropropionitrile, 33 mmoles of methyl acrylate, 27 mmoles of acrylonitrile, 70 mmoles of dimethylformamide and 5.24 'g. of water. The corresponding flow of solvent is 0.070 1./hr., and the total flow of organic reactants is 112.7 ig./hr. The flow of amalgam is 1.997 kg./hr. The amalgam contains 5.62 g. of sodium/kg. The flow of sodium is therefore 11.22 g./'hr. or 488 mg.- atoms/hr.

Every hour there is produced a mixture containing 92.5 mmoles of methyl cyanopentanoate, 218 mmoles of adiponitrile, 15.3 mmoles of dimethyl adipate, 41 mmoles of methyl B-chloropropionate, 13 mmoles of B-chloropropionitrile, 13.7 mmoles of acrylonitrile and 21.4 mmoles of methyl acrylate.

The theoretical yields calculated with respect to the two ,B-chlorinated reactants are 62.0% of methyl cyanopentanoate, 14.6% of adiponitrile and 10.3% of dimethyl adipate or a total yield of 86.9%.

The practical molar yields calculated by hearing in mind that all the reactants have reacted are respectively 57.4% of methyl cyanopentanoate, 13.6% of adiponitrile and 9.5% of dimethyl adipate or a total of 80.5%.

The yield for the three dimers calculated with respect to sodium is nearly quantitative.

What We claim and desire to secure by Letters Patent is:

1. In a dechlon'nating dimerization process for dechlorinating fi-chloro organic compounds having the formula ClCHRCHRX, in which R and R' each are a hydrogen or an alkyl group and X is a nitrile or a carboxylic acid alkyl ester group, by reacting said compounds with an amalgam selected from the group consisting of alkali metal and alkali earth metal amalgams, the improvement comprising carrying out the reaction by contacting the amalgam with a solution of said j8-chloro organic compounds in an organic solvent selected from a member of the group consisting of furfural, dimethylsulfate, dimethylsulfoxide, tetramethylenesulfone, acetamide, formamide, N-methylformamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-methylpropionamide, hexamethylenephosphortriamide and mixtures thereof.

2. Process according to claim 1, in which the fl-chloro compound is fl-chloro-propionitrile which contains from 0.001 to 1 mole of acrylonitrile per mole of fl-chloropropionitrile.

3. Process according to claim 1, in which the solvent is dimethylformamide.

4. Process according to claim 1, in which the solvent is dimethylsulfoxide.

5. Process according to claim 1, in which the fi-ch-loro organic compound is fl-chloropropionitrile.

6. Process according to claim 1, in which the ,B-chloro organic compound is methyl fl-chloropropionate.

7. Process according to claim 1, in which the quantity of the solvent is from 0.04 to 10 liters per mole of the fl-chloro organic compound.

8. Process according to claim 7, in which the quantity of the solvent is from 0.05 to 2 liters per mole of the fi-chloro compound.

9. Process according to claim 1, in which the organic solvent solution of the fi-c'hloro organic compound contains water in a quantity of 0.05 to 15% by weight based on the total weight of the solution.

10. Process according to claim 9, in which the quantity of the water is from 1 to 10% of the total weight of the solution.

11. Process according to claim 2, in which the quantity of the acrylonitrile is from 0.01 to 0.50 mole per mole of the fi-chlorinated propionitrile.

References Cited UNITED STATES PATENTS 3,215,726 11/1965 Sennewald et al. 260465.4 3,356,708 12/1967 Davies et a1 260465.8

FOREIGN PATENTS 1,436,896 3/ 1966 France.

JOSEPH P. BRUST, Primary Examiner US. Cl. X.R. 

